The girls in the bikinis are adults now, but their 1970s beachside picnic hasn't aged a day, safe on a forgotten roll of film inside a dusty old camera.

After decades dormant, the film was developed by Flinders photography enthusiast Peter de Graaff, when he bought the camera at a Thirroul junk shop last week.

Mr de Graaff wants to return the photos to the family pictured.

"All family photos are valuable," Mr de Graaff said.

"I actually came across a shoe box of my own rolls of film that hadn't been developed for 15 years, when the kids were three or four.

"It's nice to have those things - it sort of reminds you of a different time and a different place."

Mr de Graaff is a member of multiple online photography collectives, and has accumulated 43 different cameras over the years.

Sometimes he will swap a camera with another in the group to experiment and learn more about the machines.

Mr de Graaff mostly uses old film cameras bought online.

He develops film in a converted cupboard at his home, preferring the process to modern digital practices.

"[Film] has got a tangibility. You tend to be a bit more sparing about your subject matter. You might just take one or two and really try to get it right," Mr de Graaff said.

"Someone might take a huge amount of photos with [a digital camera] but they don't print any of them."

Mr de Graaff believes the forgotten family picnic occurred near the lagoon at North Beach. He estimates the shots were taken in the early 1970s, based on the style of cars pictured in some backgrounds.

The photos were taken on a Ferrania Euralux 44 plastic camera, regarded as one of the first plastic toy cameras. Mr de Graaff consulted another photography enthusiast overseas for advice on how long to soak the film, before deciding on 10 minutes.

"I was very surprised that the film wasn't completely fogged up."

Mr de Graaff asked that the pictured family make contact with the Mercury in order to reclaim the photos. Email scoop@illawarramercury. com.au with relevant information.